1. Field of the Invention
The invention relates to a decision feedback equalizer, and in particular, to a tap/group-revivable decision feedback equalizing method and equalizer using the same.
2. Description of the Related Art
In a communication system receiver, an equalizer is generally designed to eliminate multipath distortion to avoid signal distortion.
Referring to FIG. 1, a schematic diagram illustrating a decision feedback equalizer 10 of prior art is shown. The decision feedback equalizer 10 comprises a feed-forward filter 102, a feedback filter 104, a subtractor 106 and a slicer 108. The feed-forward filter 102 generates a pre-cursor signal t2 from a received input t1. The subtractor 106 subtracts a post-cursor signal t3 output by the feedback filter 104 from the pre-cursor signal t2 to generate an equalizer output t4. Then, the slicer 108 utilizes the equalizer output t4 to generate a decision output t5, which is fed to the feedback filter 104 so as to generate the post-cursor signal t3.
Referring to FIG. 2, a schematic diagram illustrating the feed-forward filter 102 and the feedback filter 104 of FIG. 1 is shown. The feed-forward filter 102 has M*m taps divided into M groups, wherein each group of the M groups has m taps. For example, there is a group 0 having a tap 0, a tap 1, . . . , and a tap m−1. On the other hand, the feedback filter 104 has N*n taps divided into N groups, wherein each group of the N groups has n taps. For example, there is a group 0 having a tap 0, a tap 1, . . . , and a tap n−1. Each tap of the feed-forward filter 102 or the feedback filter 104 has a corresponding tap coefficient.
In prior art, the taps of any of the groups of the feed-forward filter 102 or the feedback filter 104 may be selected and utilized for equalization depending upon whether a tap coefficient of the taps of any of the groups is greater than a predetermined value. If a tap coefficient of any of the groups is greater than the predetermined value, all the taps of any of the groups will be selected and utilized for equalization. Otherwise, all the taps of any of the groups will be dismissed and no longer be selected and utilized for equalization. However, since multi-path distortion may vary with time, the taps of any of the dismissed groups at a specified time due to dramatic multipath distortion may be useful at another specified time with normal multipath distortion. Thus, time-invariantly discarding the taps of any of the groups without a tap coefficient greater than the predetermined value can cause performance degradation of the equalizer 10.